OS X Mountain Lion AirPlay Mirroring does not work on older Macs

One of the more than 200 new features in OS X Mountain Lion is AirPlay Mirroring, which allows you to send what’s on your Mac screen wirelessly to Apple TV with a resolution of up to 1080p HD. AirPlay Mirroring will scale the content of your Mac screen to fit the HDTV resolution, using an encrypted stream. You can use it to mirror your presentation slides on your Mac, play your movie or music on your Mac and enjoy them on your HDTV home theatre setup.

AirPlay MirroringRequires a second-generation Apple TV or later. Supports the following Mac models:

iMac (Mid 2011 or newer)

Mac mini (Mid 2011 or newer)

MacBook Air (Mid 2011 or newer)

MacBook Pro (Early 2011 or newer)

All AirPlay Mirroring supported Mac models are using at least Intel’s Sandy Bridge processor. This suggests that AirPlay Mirroring is using some feature in the newer Intel processor to offload the video encoding required, without any CPU or GPU tied up. You might notice that not a single Mac Pro is in the list.